richardh
spending too much on rocks
Member since June 2016
Posts: 391
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Post by richardh on Nov 5, 2016 19:52:40 GMT -5
I have been getting quite confused trying to figure it out. This really came to a head when I visited a friend who recently purchased a bunch of different types of agates. Probably the most confounding there the Lake Superior Agates. Some of them were the “fortification” type with all the squiggly lines that I always associated with agates and others looked like nothing more than some crummy looking off-white quartz with lots of pits and holes in it. The same goes for some agate that was sold under the name “Brazilian Agate.” Again, some of it has the familiar fortification lines and some of it was just some semi-transparent off-white material that was very uninteresting and reminded me of quartz that I picked up off the ground while visiting New Hampshire last summer.
To make things even more confusing I received some “Rio” agate from Mel here on this website. The material is large cobbles and when I cut into them they look like some brown/orange patterns that look sort of like dead moss. I’m guessing that this is what is called moss agate.
I was recently down in south Texas and picked up some “biscuits” along the Rio Grande. I cut several of them open before my tile saw literally caught on fire and what I saw inside was something I can’t begin to classify.
One of them looked almost exactly like the material I received fro Mel with the brown/orange moss. Others looked pretty much exactly like what I have been collecting around west Houston and calling chert. It is tan/gray/brown opaque material, sometimes with some nice bands/lines in it but not colorful and not translucent at all. There are some others that are partially made of what looks to me like chert and partially made out of semi-transparent quartzy-looking cells.
Anyway, if anyone could point me in the right direction I would very much appreciate it.
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Post by Pat on Nov 5, 2016 21:34:17 GMT -5
There is a beautiful new book out: Agates by Pat McMahan. Loaded with gorgeous agates from all over. $130 on Amazon.
Good luck!
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richardh
spending too much on rocks
Member since June 2016
Posts: 391
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Post by richardh on Nov 5, 2016 22:08:01 GMT -5
I'm sure that book is fantastic but way out of my budget at the moment. I'm struggling just to keep the minimum equipment going. It looks like the book has tons of fantastic images but I think many of them are the sorts of rocks that I will never find in the wild.
I guess what I really want to know is what actually makes a rock an agate. I would also like to eventually figure out if a rock I encounter is an agate or not. I don't think I have much hope of doing the second if I don't know the first.
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Sabre52
Cave Dweller
Me and my gal, Rosie
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Post by Sabre52 on Nov 5, 2016 22:16:39 GMT -5
Probably oversimplification but: Agate is translucent to semi translucent chalcedony (cryptocrystalline quartz) which shows a variety of colorful formations of bands, lines or mineral inclusions ie plumes, moss, orbs etc. Jasper- agate is chalcedony that has colorful opaque inclusions and areas of translucent chalcedony. Jasper is opaque cryptocrystalline quartz with fibrous inclusions....Mel
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richardh
spending too much on rocks
Member since June 2016
Posts: 391
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Post by richardh on Nov 5, 2016 22:56:18 GMT -5
Thanks Mel
So the difference is basically that agates are transparent/translucent? What's the difference between agate and Quartz?
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dottyt
spending too much on rocks
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Post by dottyt on Nov 5, 2016 23:00:22 GMT -5
The material is large cobbles and when I cut into them they look like some brown/orange patterns that look sort of like dead moss. If you don't care for that you can send it this way! I think Mel gave the standard shortish definition of "agate." I don't think any destination would help you self collect them though, as they often only show their true beauty when cut. I think you would have to find someone local to take you to a place where they are found and then show you what they look like there. I guess the Lakers and some others where the rind is worn down would be an exception to this. Hope your saw is okay! Your new avatar looks great. Big improvement on the generic one you were using before! P.S.: Agate is a specific type of quartz. As you no doubt know, many rocks are made of quartz and there are also single crystals of quartz. In agate the quartz is formed into layers.
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richardh
spending too much on rocks
Member since June 2016
Posts: 391
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Post by richardh on Nov 5, 2016 23:14:10 GMT -5
Dottyt I'm very sorry if I gave the impression that I was somehow disappointed with the material I received from Mel. I'm actually VERY excited about it and it has been driving me crazy not being able to finish tumbling them.
I would definitely recommend the material from Mel to anyone who is interested in some neat material to tumble or otherwise work with.
If I can get a working saw before the traveling rock box comes my way I will put a couple of slabs of it in.
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Post by adam on Nov 6, 2016 7:58:26 GMT -5
Wow, you have a saw. Yet you're confused when it comes to agates. I'm sure you'll figure it all out, but, damn, tons of people don't have the money for such a luxury as a slab saw or trim saw. I'm jealous. Very jealous.
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Post by Peruano on Nov 6, 2016 7:59:55 GMT -5
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richardh
spending too much on rocks
Member since June 2016
Posts: 391
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Post by richardh on Nov 6, 2016 10:39:52 GMT -5
Wow, you have a saw. Yet you're confused when it comes to agates. I'm sure you'll figure it all out, but, damn, tons of people don't have the money for such a luxury as a slab saw or trim saw. I'm jealous. Very jealous. I wish I had a trim saw or slab saw. I *had* a Skil tile saw that unexpectedly caught on fire and burned up while I was trying to cut some of my rios. I looked on line and it was about an $80 saw which in the scheme of lapidary is pretty inexpensive. I hope to replace it before too long but at this moment I'm just thrilled to have my tumbler working again. My confusion about agates is that there doesn't seem to be an agreed upon definition about what one is. Sort of how planets were before the astronomers got together and created a uniform definition and as a result kicked Pluto out of the planet club. Maybe that isn't accurate and there actually is a uniform definition and if there is I hope to find out what it is. Just to beat a dead horse a little when I was taking life science in school we were taught that there were a certain set of characteristics shared by all mammals and no other creatures making it possible to determine if an organism is a mammal or not. They must be warm blooded, have hair, feed their young milk (have mammary glands)... I know it seems anal but I get curious about these things when I see so many seemingly different things called agates.
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richardh
spending too much on rocks
Member since June 2016
Posts: 391
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Post by richardh on Nov 6, 2016 11:18:12 GMT -5
Great link and very interesting and informative read. Thanks for posting it.
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panamark
fully equipped rock polisher
Member since September 2012
Posts: 1,343
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Post by panamark on Nov 6, 2016 12:50:35 GMT -5
Richard, first a shout out to fellow birder!
Anyway, to add to Mel's description, yes in general the differentiation between agate and jasper now seems to be whether the material is transparent (agate) or opaque (jasper). As I understand it "agates" originally HAD to have either fortification bands or moss/dendrites. So even clearish chalcedony was not considered agate. Now the distinctions are not so clear (ha)
I think the popularity of rockhounding, and more likely the increase in prices of material inflated the label of agate. Heck, even the label jasper has been inflated to include some rhyolites that are pretty. The names went from a geological basis, to a marketing basis. Welcome to the rockhound world. BTW: the simple definition of "mammal" is frought with many interesting exceptions
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richardh
spending too much on rocks
Member since June 2016
Posts: 391
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Post by richardh on Nov 6, 2016 12:58:14 GMT -5
Thanks for the additional input, very interesting to say the least. At least I don't feel quite as dumb for being confused.
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Post by 1dave on Nov 6, 2016 13:14:27 GMT -5
AgateFrom Penn State News - 2001Baker Mine, New Mexico - Thunderegg in spheroidal rhyolite. Argentina - irregular Amygdaloid in andesite. Brazil - Amygdaloid steam pocket in basalt. ADMIN EDIT - fixed broken images
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Post by drocknut on Nov 6, 2016 13:28:30 GMT -5
Watch out that you don't ask how agates form, that will open up a totally new can of worms so to speak. There are so many theories out there but no one really knows for certain. Also, there were several noted RTH members who created an index of agates and jaspers from all over using pictures of them from their own stock and other RTH members. I don't have the link and can't find it but at one time it was online. Perhaps someone could steer you in the direction of it.
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richardh
spending too much on rocks
Member since June 2016
Posts: 391
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Post by richardh on Nov 6, 2016 13:32:06 GMT -5
Great read 1Dave! Thanks for posting it.
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richardh
spending too much on rocks
Member since June 2016
Posts: 391
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Post by richardh on Nov 6, 2016 13:33:30 GMT -5
Watch out that you don't ask how agates form, that will open up a totally new can of worms so to speak. There are so many theories out there but no one really knows for certain. Also, there were several noted RTH members who created an index of agates and jaspers from all over using pictures of them from their own stock and other RTH members. I don't have the link and can't find it but at one time it was online. Perhaps someone could steer you in the direction of it. Thanks, I did run across that thread which was part of what drove me to ask the question. Very interesting stuff!
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Post by Lapidaryrough / Jack Cole on Nov 6, 2016 14:23:59 GMT -5
silicates in solution filling low pressure zone. from the base of your feet to about 3.5 kilometers. Orthoclase zone of the lithosphere.
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Post by 1dave on Nov 6, 2016 17:19:09 GMT -5
Watch out that you don't ask how agates form, that will open up a totally new can of worms so to speak. There are so many theories out there but no one really knows for certain. Also, there were several noted RTH members who created an index of agates and jaspers from all over using pictures of them from their own stock and other RTH members. I don't have the link and can't find it but at one time it was online. Perhaps someone could steer you in the direction of it.
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richardh
spending too much on rocks
Member since June 2016
Posts: 391
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Post by richardh on Nov 6, 2016 23:01:58 GMT -5
silicates in solution filling low pressure zone. from the base of your feet to about 3.5 kilometers. Orthoclase zone of the lithosphere. It’s difficult for me to imagine how being underneath 3km of sediment is low pressure but of course it’s all relative. When I try to imagine how agates might form and how long it takes it is sort of mind bending. I was also very impressed when I read that Lake Superior agates formed over a billion years ago. The number is so big I don’t think I can even comprehend it. Anyway I really appreciate everyone taking the time to humor me on this question.
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